1. Field of the Invention
The invention relates to means for positioning logs in a disc type log chipper.
2. Problem
Disc type wood chippers for reducing logs and the like to usable chips for the paper pulp industry are well known. Generally, the chipping process includes debarking cut trees and then cutting the trees into chips for further processing into pulp from which paper is made. In the formation of the chips, debarked logs are fed into a disc chipper which includes a plurality of cutters such as knives that are mounted within recesses in the disc and adjacent to wear plates disposed on the disc. The knives cut chips from the incoming logs and pass the chips through radial openings in the disc.
3. Prior Art
While generally successful, such disc type chipping machines have suffered from certain deficiencies. Notable among the deficiencies is the difficulty in cutting chips from large diameter logs. The power requirements for chipping large diameter logs are a great deal more than for chipping smaller logs. Heretofore, it has been quite uneconomical to employ disc chipping machines that are sufficiently powerful so that they are capable of continuously chipping large diameter logs at the desired chipping rate for smaller logs.
Because of the high power demand for cutting large diameter logs quickly, attempts have been made in the past to make disc chippers more responsive to varying sizes of logs and the consequent power requirements for chipping logs of large diameter. Since most power companies charge not only according to the amount of power consumed, but also according to the peak load, the cost associated with chipping large logs can be very high. This situation is of special importance if the chipping is taking place at a remote location where producing the necessary power is very difficult.
Such prior art attempts have included elaborate means for detecting a deceleration of the disc chipper due to the load imposed on the chipper by a large diameter log. Upon the detection of deceleration, the advance of the log is halted by a discontinuation of power to the log feeding belt and by holding the log in this halted position by a complicated hydraulically operated swing arm. Additional drawbacks to this type of chipping operation are the necessary inclusion of a complex feed mechanism to the disc chipper. The feed mechanism is subject to mechanical and electrical repairs and maintenance, which adds to the total cost of chipping logs. Furthermore, a system of this type is heavier and larger than a disc chipper without the additional log feed machinery. This makes it more difficult to move a disc chipper of this type into remote locations. This prior art system has been implemented for some portable chipping applications, but large diameter log chip quality using this system usually suffers due to the frequent stopping of the log. Furthermore, the upstream feed of logs to the chipper disc must be halted whenever the swing arm is activated. Halting the upstream feed of logs drastically slows down the chipping operation, and in some cases is very difficult to control.
Other prior art attempts have included the complicated use of control means for reversing the operation of the feeding rollers of the disc chipper. The control means comprise sensing means for monitoring the speed of the disc and the use of electric valves and time relays to control hydraulic motors in the forward and reverse directions. Through the use of this type of disc chipper, there is less likelihood of chipper deceleration, and a system of this type does diminish the power requirements in bringing the disc up to speed after a deceleration. However, the control systems for a disc chipper and log feed mechanism of this design is of such complexity that a highly skilled technician would be necessary to repair a disc chipper of this type. There would also be a substantial investment for machinery of this type. Due to the halting of the feed of logs to the chipper, the swing arm log stopper system and the feed monitoring system are both inadequate for large scale chipping operations that require more than one log at a time to be fed to the chipper. Halting the upstream log feed becomes too costly and difficult for such large scale applications.
Still other prior art disc chippers have incorporated other complex machinery to make chippers responsive to the increased power requirements of chipping large diameter logs. Attempts at saving power have also included the use of heavy flywheel attachments to the disc shaft. This type of machinery allows the use of a lower horsepower motor than needed otherwise. However, this type of chipper is limited to handling large diameter logs that are short, i.e., six to eight feet in length. Another drawback is that discs with flywheels spend more power to accelerate up to speed.
4. Additional Power Problem
A related power problem within the design of disc chippers is the number of knives on a given disc. The production rate for a disc chipper is primarily determined by the rate at which small diameter logs are processed. By doubling the number of knives on a given disc, the production rate for these small logs is doubled. Unfortunately, it is the amount of power required to chip the largest diameter logs that usually determines the number of knives on the disc, since the large diameter logs determine the peak power requirements. So, even though a designer may desire the higher production rates of a disc with many knives, ultimately the designer is limited by the high power requirements of chipping large diameter logs.
For the foregoing reasons, there is a need for a disc type log chipper that is capable of continuously chipping large diameter logs without being so powerful that it is uneconomical to operate. There is also a need that the entire disc chipper system, including log feed mechanism, be inexpensive to manufacture, simple in its construction, and both as small and light as possible to permit utilizing the chipper at a remote location.